Antioxidant compositions



United States Patent 3,3857% ANTHUXTIDANT QOMPGSITIONS Henry Menrig Davies, Rogerstone, Newport, and Arthur damuci Thomas, Newport, England, assignors to Monsanto ompany, a corporation of Delaware No Drawing. Fiied Apr. 22, 1%6, Ser. No. 544,406 Claims priority, application Great Britain, Apr. 27, 1965, 17,634/65 7 Claims. (Cl. 252-325) ABSTRACT @F THE DESCLOSURE Compositions which exhibit improved lubricating oil qualities and a reduced tendency towards pitting of metal members by the incorporation of an aikenylsuccinic compound-polyamine reaction product, a Group II metal dithiophosphate at a minimum concentration of about 1% and an aralkyl phenol into a lubricating oil. The compositions can be utilized for the lubrication of internal combustion engines.

This invention relates to antioxidant compositions to the use of antioxidant compositions in lubricating oils.

When conventional lubricating oils are subjected to high operating temperatures for prolonged periods of time, they show a tendency to undergo oxidation and decomposition. As well as having a generally adverse efiect on the quality and lubricity of the oil, the precesses of oxidation and decomposition can give rise to acidic substances that have a corrosive action on metal with which the lubricating oil comes into contact.

A Wide variety of materials have been proposed or used as additives in lubricating oils to counteract the effects of the oxidation of the oil, including certain metal derivatives of dithiophosphoric acids, in particular zinc dialkyl dithiophosphates.

Dithiophosphates of this type are believed to act both as antioxidants by decelerating the normal process by which the oil is oxidized, and as corrosion inhibitors by an interaction with metallic surfaces. However, there is associated with the use of dithiophosphates a tendency for adverse side effects to develop, among which are piston ring sticking and metal pitting. Such side effects become more pronounced as the temperature to which the oil is subjected increases, and are also more pronounced when the dithiophosphate is used in conjunction with certain deter ent-type additives.

We have now found that lubricating oil compositions containing metal dithiophosphates singly or in conjunction with detergent-type additives can be stabilized against adverse side effects by incorporating into the lubricating oil compositions a phenolic compound selected from (a) An aralkyl phenol represented by the structure R1 LR. K

and (0) mixtures of (a) and (b); wherein R and R each are selected from the group consisting of alkylene and alkenylene; R and R each are independently selected from the group consisting of hydrogen, alkyl, aryl, substituted alkyl, substituted aryl, halogen, nitro and aralkyl; R R R and R each are selected from the group consisting of hydrogen, alkyl, halogen, nitro, phenyl and substituted phenyl, provided that when any one of R R R and R is hydrogen the group represented by R phenylR- and R phenylR can occupy that position relative to the phenolic hydroxyl that is occupied by hydrogen; n and m are whole numbers having a value of 1 to 2; and R is alkyl having from 8 to 24 carbon atoms.

In addition, the present invention relates to antioxidant compositions comprising an oil-soluble metal derivative of a diester of dithiophosphoric acid and a phenolic compound as set out above.

The invention also includes lubricating oil compositions comprising a lubricating oil and a minor proportion of an antioxidant composition of this invention.

The presence of a phenolic compound in a lubricating oil composition as defined above is of particular value Where the amount of the dithiophosphate present in the composition is at least 1% of the total weight of the composition and, in addition, where the composition contains an alkenylsuccinic anhydride-amine reaction product as a detergent additive.

The preferred metal derivatives of diesters of dithiophosphoric acids and the preferred phenolic compounds for use according to the present invention are respectively the zinc dialkyldithiophosphates and the bis(u-methylbenzyl) derivatives of phenol and 4-alkyl-substituted bis (er-methylbenzyl) derivatives of phenol.

The oil-soluble metal derivatives of diesters of dithiophosphoric acid, hereinafter refered to as dithiophosphates, are compounds that are normally represented by the formula:

wherein R and R are each selected from the group consisting of alkyl, cycloalkyl, aralkyl, aryl, substituted aryl and substituted alkyl, 0 is a whole number having a value of 1 to p, p is the valence of M and M represents a metal atom.

The preferred dithiophosphates are those compounds wherein R and R are each alkyl radicals containing at least 3 carbon atoms, preferably containing from 3 to 20 carbon atoms, said alkyl radical having either a straight or branched chain. Typical examples of alkyl radicals are isopropyl, isobutyl, n-pentyl, n-hexyl, 4-methylpent-2-yl, l-methylhexyl, n-octyl, 2-ethylhexyl, n-decyl, n-dodecyl, n-tetradecyl and cetyl.

Typical examples of cycloalkyl radicals wherein either R or R or both are cycloalkyl are cyclohexyl and methylcyclohexyl. Typical aralkyl radicals are benzyl and phenyl-substituted alkyl radicals wherein the alkyl radical contains at least 3 carbon atoms. Typical examples of substituted aryl compounds are alkylphenyl wherein the alkyl substituent contains from about 3 to 20 carbon atoms.

With regard to the metal, the derivatives of diesters of dithiophosphoric acid are generally those of metals of Group II of the Mendelyeev Periodic Table, for instance, calcium, barium, cadmium and Zinc. Zinc, however, is the preferred metal.

In addition to the metal dithiophosphates wherein 0 is the valence of M, it has also been found that the basic salts of dithiophosphates are also useful and contemplated within the scope of this invention. Thus, when 0 is a number less than the valence of M, that is, p, there can be formed a basic salt with a diester of dithiophosphoric acid. A typical example of a basic salt would be a zinc hydroxide dialkyl dithiophosphate.

The oil-soluble metal derivatives of diesters of dithiophosphoric acid are normally prepared by the action of the appropriate alcohol or mixture of alcohols on phosphorus pentasulfide in proportions such that the product is a diester acid, which in turn is neutralized by reaction with an oxide, hydroxide or carbonate of the required metal.

Specific examples of the oil-soluble metal derivatives that are useful according to the present invention are the zinc derivatives of the following dithiophosphoric acids: diisopropyl; diisobutyl; di-sec-amyl; di-n-hexyl; di(l,3- dimethylbutyl); isopropyl, 2-ethylhexyl; isobutyl, 2-ethylhexyl; di(2-ethylhexyl); isopropyl, n-decyl; sec-butyl, cyclohexyl; dicyclohexyl; isopropyl, 3-phenylpropyl; and di(p-l,1,3,3-tetramethylbutylphenyl) The preferred aralkyl phenols represented by (a) are those in which at least one aralkyl group is present in an ortho position relative to the phenolic hydroxyl group. Thus, the preferred aralkyl phenols are those phenolic compounds wherein n is 2, R and R are hydrogen and the aralkyl group occupies either the 2, 4 or 2, 6 position in relation to the phenolic hydroxyl group.

In general, it is preferred that R and R are alkylene and that the number of carbon atoms in the alkylene group does not exceed four. Typical examples of the groups R -phenylR and R phenylR are phenylethyl, tolylethyl and phenylpropyl, phenyl n-alkylene and groups containing a secondary or tertiary carbon linking atom as, for example, u-methylbenzyl, a-ethylbenzyl and a,a-dimethylbenzyl. When n and m have a value of 2, the groups R phenylR and R phenylR can be different with respect to the substituents R and R Typical example of the two groups represented by R phenylR- and R -phenyl-R which are attached to the same phenol nucleus are tolylethyl and xylylethyl.

Although the aralkyl phenol compounds as represented by (a) have been found to inhibit and control the adverse side effects of lubricating oil compositions containing dithiophosphates, it has been found that the aralkyl 4-alkyl phenols represented by (b) are more effective apparently due to the 4-alkyl group. The 4-alkyl group imparts better oil solubility to the phenolic compound and in addition provides greater oil solubility to the phenolic compound as the phenolic compound acts as an inhibitor in lubricating oil compositions. Thus, it has been found that an alkyl group containing at least 8 carbon atoms and up to 24 carbon atoms provide excellent oil solubility and enhanced properties to the aralkyl phenol compounds.

The alkyl group, that is, R can be arranged in either a straight or branched chain. Examples of such alkyl groups are octyl, nonyl, dodecyl, tridecyl, tetradecyl, pentadecyl and octadecyl groups. In practice, the alkyl group is often one derived from an alkylate fraction, for example, an octyl group corresponding to diisobutylene, a nonyl group corresponding to propylene trimer, or a dodecyl group corresponding to propylene tetramer or triisobutylene. Such alkylate fractions are in some instances isomeric mixtures, and where this is so the alkylated derivative of aralkyl phenols are correspondingly heterogeneous. Such mixtures are, however, fully comparable in performance with the pure aralkyl 4-alkyl phenols while having economic advantages over the latter.

In general, the phenolic compounds represented by (a) and (b) which are preferred are those in which R R R and R are hydrogen. However, compounds containing one or more additional hydrocarbon substituents in the 3 or 5 position relative to the phenolic hydroxyl group are also effective and contemplated within the scope of this invention. Such a substituent is normally an alkyl group, for example, a methyl, ethyl, or propyl group,

and a typical example of a compound represented by (a) is 2,4-diara1kyl-m-cresol. In addition, the 3, 5 substituent can be alkenyl, for example, allyl, or an aryl group, for example, phenyl or tolyl. In general, it has been found that the 3, 5 position in relation to the phenolic hydroxyl group is a non-interferring position, that is, there is in general no advantage in having this position occupied by any substituent. It is, therefore, preferred that the 3, 5 position is not occupied by any substituent although such substituent does not adversely affect any of the properties of the phenolic compound as represented by (a) and (b).

Specific examples of phenolic compounds that can be used according to the present invention are 2,4-biS(ozmethylbenzyl) phenol, 2,6-bis(a-methylbenzyl) phenol, 2,6-bis(ix-methylbenzyl) 4(l',l',3' tetramethylbutyl)- phenol, 2,6 bis(a,a-dimethylbenzyl)-4(l,l',3,3'-tetramethylbutyl) phenol, 2,6-bis(a-rnethylbenzyl)-4(4,4'-dimethylhept-2-yl) phenol and 2,6-bis(a-methylbenzyl)-4- dodecylphenol. The dodecyl group in the last-named phenolic compound can be conveniently derived from propylene tetramer.

In the lubricating oil compositions of this invention, the base oil is normally a hydrocarbon oil, and can be in addition dicarboxylic acid esters such as 2-ethylhexyl sebacate, alkylated benzene, alkylene oxide polymers, silic-ate esters, silicone polymers and the like or mixtures thereof.

Usually the hydrocarbon oil is of mineral origin, although it can be synthetic, for instance a polyolefin. The oil base may also contain an oil of animal or vegetable origin, for example, lard oil or castor oil.

While the presence of the phenolic compounds as represented by (a) and (b) in a lubricating oil composition of this invention is particularly adapted to deal with problems that arise where the metal derivative of the dithiophosphoric acid is present in lubricating oils at a level of about 1% by weight, beneficial effects are also apparent where the dithiophosphate forms a smaller proportion of the total composition. Generally the dithiophosphate will be present in an amount of from about 0.10 to about 10% by weight of the total composition.

The phenolic compound of this invention is normally present in lubricating oil compositions in an amount varying from about 0.05 to about 10% of the total weight of the composition, preferably from about 0.05 to about 4%.

The concentrates and antioxidant compositions of the invention are, of course, intended for addition to lubricating oils, and the relative proportions of the antioxidants in these mixtures are therefore selected according to the proportions required in the lubricating oil composition.

The proportion of oil in the concentrates of the invention can vary from, for example, 20% to of the total weight of the concentrate.

The antioxidant compositions, concentrates and lubricating oil compositions of the present invention can optionally contain other additives having beneficial effects on the properties of the oil. Such additives include for instance materials having detergent properties, for example, oil-soluble alkaline earth metal derivatives of phosphosulfurized polyolefins, alkali or alkaline earth metal salts or petroleum of alkylbenzene sulfonates or ashless detergents, for instance alkenyl-succinic anhydrideamine reaction products, anti-wear additives, for example, aryl phosphates such as for instance tricresyl phosphate, viscosity improvers and pour-point depressants.

The alkenylsuccinic anhydride-amine reaction products referred to above are usually derived from alkenylsuccinic anhydrides wherein the alkenyl group contains a relatively large number of carbon atoms. These anhydrides are generally made by the direct action of a polyolefin on maleic anhydride, suitable polyolefins being low polymers of C to C olefins, for instance, polypropyle-nes, polybutylenes or polyisobutylenes. The alkenyl group contains generally from 50 to 200 carbon atoms. The amines with which the alkenylsuccinic anhydrides are reacted are in most instances aliphatic polyamines, especially polyalkylene-polyamines such as for instance diethylenetriamine In a further test, Formulations A and B were compared as lubricants in the Petter W. l gasoline engine test run under I.P. 176/65 conditions. The temperature in the undercrown region during operation of the engine was and tetraethylenepentamine. Also belonging to the class 5 255 C. The performance of th lubricating oil was of ashle-ss detergents or dispersants for lubricating oils are assessed by i ton d rown nd ki t ting th aid alkenylsuccinic anhydride-amine reaction products modiratings being determined by visual inspection, and being fied by the use of a third component, for example, as represented by a figure on a scale from 0 to 10 where 0 described in United States Patent 2,563,876 corresponds to extremely dirty and 10 to perfectl clean. Ashles detergents of the above type may be used in 10 A third comparison was made between the increases in lubricating s at a range of concentrations, being present the viscosities of the oil formulations that occurred durin amounts of, for example, from about 0.1 to 5% i th period fth P tt engine te t. of the total weight of the composition. When there is also F th results given i th f ll i bl h fen-nupresent a metal dithio phosphate, the advantages to be lation containing the aralkyl phenol is again shown to be gained by also inculding a phenolic compound in the lubrisuperior, eating oil composition becomes particularly apparent TABLE H where the amount of the alkenylsuccinic anhydride-amine reaction product is about 1.25% or more of the total weight a??? ag??- of the composition.

The invention is illustrated by the following non-limit" i iitfifi323%35;aunt:3231;133:1333: 813 iii ing examples. Percent increase in viscosity of formulation 20.7 26.9

This example descri i t lle gl o du ction of an antioxidant EEXAfMPLE 2 composition and lubricating oil composition according to .Thls fpf 'descnbeis produqtlon f a lubncamg the invention and illustrates the improved performance 011 cofnp 031mm according to mvennon com- I ts effect on the Wear of ch1lled ta ets W1th that of such an 011 composition in comparison with a similar i f 1 pp 1k h 1 lubricating oil not containing a phenolic compound. 0 er f i contamflig am 1 cno An antioxidant composition was prepared by mixing a p g f m e 'composmon (ljqormu anon C) zinc isopropyl Z-ethylhexyl dithiophosphate with bis(rxaccording tot e mventlon Wfire as follows methylbenzyl) phenol containing the 2,4-isomer as the Parts y j major component, in the proportions by weight of 5 M detergent as FormulatlPn A 1) Parts to 1 part Z nc 1sopropyl Z-ethylhexyl dithiophosphate 1.0 A lubricating oil formulation (A) having the following Bl s("mefl?ylbenzyl). P composition was then prepared: Mineral 011 of lubricating viscosity 94.0 Formulation A: Parts by weight A formulation was prepared in which the amounts of Mixed detergent containing barium and caldetergent and dithiophosphate additives were the same as .cium sulfonates and an alkenylsuccinic in Formulation C but the bis(a-methylbenzyl) phenol anhydride-polyalkylenepolyamine reaction was omitted, the proportion of mineral oil being inproduct 4.75 49 creased correspondingly (Formulation D). Antioxidant composition 1.5 The results obtained in an examination under standard Mineral oil of viscosity 11 centist'Okes at conditions of the effects of the various formulations on 210 F. 93.75 chilled tappets are given below. and for comparison, a formulation (B) having the fol- TABLE III lowing composition, i.e., one containing the same amount Formulation: Corrosive wear of the zinc dialkyldithiophosphate as Formulation A.: Less than 10% pitting. Formulation B: Parts by Weight D Very badly pitted- M-ixed detergent as in Formulation A 4.7 Comparison of the behavior of Formulations C .an D Zinc isopropyl Z-ethylhexyl dithiophosphate 1.25 shows that this adverse effect is substantially reduced by Mineral oil of viscosity ll centistokes at including phenolic compounds in the formulation.

210 F. 94-0 0 EXAMPLE 3 In one comparison of the two formulations, each was An antioxidant composition was prepared by mixing a used in turn as the lubricant in a 4-cylinder gasoline Zinc isopropyl Z-ethylhexyl ditlziophosphate and a 2,6- engine. In each test, the engine was run at normal opbis(ct-methylbenzyl)-4-nonyl phenol in the proportions er-ating temperature (275 C. in the ring belt area), and by weight of 5 parts to 1 part. This mixture was used in the pistons (each of which carried two piston rings) and producing a lubricating oil formulation having the folcylinders were examined after continuous operation for lowing composition: hours. Parts by weight The following observations were recorded. Mixed detergent as in Formulation A (Ex. 1) 4.75

TABLE I Formulation No. 1 Piston No. 2 Piston No. 3 Piston No. 4 Piston A All Rings Free B Both rings free Ton ring tight. Top ring tight. Top ring stuck.

Bottom ring Bottom ring Bottom ring free. free. stuck.

The beneficial effect of the aralkyl phenol in reducing Antioxidant composition 1.5 the amount of deposit formation in the piston ling belt Mineral oil of viscosity 12.7 centistokes at area is apparent. 210 F. 93.75

TABLE Iv.100 HOURS TEST DURATION Formulation No. 1 Piston No. 2 Piston No. 3 Piston N o. 4 Piston Example 3 All Rings Free B Both rings from... Top ring tight. Top ring tight. Top ring stuck.

Bottom ring Bottom ring Bottom ring free. free. stuck.

The formulation as represented by Example 3 was continued for an additional 100 hours and at the termination of the 200 hour test period it was found that all of the piston rings were free. Formulation B could not be continued for an additional 100 hours due to the overall condition of the rings that existed at the end of 100 hours.

As is demonstrated by Table I, Table II, Table III and Table IV, the incorporation of the phenolic compound inhibits and controls the adverse side effects which are present in lubricating oil formulations containing a dithiophosphate singly or in combination with an ashless detergent. The performance of the dithiophosphate with respect to pitting and ring sticking is greatly improved when a phenolic compound is incorporated into the dithiophosphate compositions. The phenolic compounds by themselves do not provide the overall qualities as provided by the metal dithiophosphates. Thus, the combination of the two additives, that is, dithiophosphates and a phenolic compound, provides lubricating oil formulations which have enhanced properties with respect to the lubrieating qualities that are needed in lubrication of moving parts. As is noted from these results, the ratings of the various piston rings showed that all rings were free at the end of the 100 hour duration. This is of significance in that the rings provide the seal between the piston and cylinder wall which is necessary in order to maintain compression within the cylinder. In addition, the rings prevent oil which is on the cylinder walls from reaching the combustion cylinder. Lubricating oil formulations in general have been found to require the dithiophosphates and ashless detergents to enhance and provide other properties of a lubricating oil formulation. It is of particular importance with respect to this invention that the presence of phenolic compounds in no way detracts from the overall properties which are provided by a dithiophosphate and ashless detergent compositions.

As is noted from Table IV the test duration was continued for an additional 100 hours which significantly demonstrates the increased effectiveness of the aralkyl 4 alkyl phenol compounds in inhibiting and controlling the adverse side effects of the dithiophosphates. The presence of the oil-solubilizing 4-alkyl group provides superior performance in compositions comprising a zinc dithiophosphate singly or in combination with an ashless detergent. This is of particular importance since it provides lubricating oil compositions which continue to provide efficient lubrication over extended periods of time.

While this invention has been described with respect to various specific examples and embodiments, it is understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

What is claimed is:

1. A composition comprising a major amount of a lubricating oil and (A) from about 0.05 to about %v by weight of a phenolic compound selected from the group consisting of (1) an aralkyl phenyl represented by the structure 8 (2) an aralkyl 4-alkyl phenol represented by the structure and (3) mixtures of (1) and (2) wherein R and R each are selected from the group consisting of alkylene and alkenylene having from about 1 to about 4 carbon atoms; R and R are each selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, alkaryl, halogen and nitro; R R R and R are each selected from the group consisting of hydrogen, alkyl, alkenyl, halogen, nitro, aryl, alkaryl and :aralkyl, provided that when any one of R R R and R is hydrogen the group represented by R phenyl-R and can occupy that position relative to the phenolic hydroxyl that is occupied by hydrogen; n and m are each whole numbers having a value of from 1 to 2; and R is alkyl having from 8 to 24 carbon atoms;

(B) from about 1 to about 10% 'by weight of a metal derivative of dithiophosphoric acid represented by the structure wherein R and R are each selected from the group consisting of alkyl having from 3 to 20 carbon atoms, cycloalkyl, aryl, aralkyl and alkaryl wherein the said alkyl portion of the aralkyl and alkaryl groups has from 1 to 20 carbon atoms; 0 is a whole number having a value of 1 to p; p is the valence of M and M represents a Group II metal atom; and

(C) from about 0.1 to about 5% by weight of a product prepared by the reaction of an alkenylsuccinic compound having from 50 to 200 carbon atoms in the alkenyl portion and a polyamine conforming for the most part to the structure .t K it).

wherein n is an integer having a value of from 1 to 10, A and A each are selected from the group consisting of hydrocarbyl and hydrogen and A and A can together form the remainder of a heterocyclic ring; and R is alkylene containing from 1 to 8 carbon atoms.

2. A composition of claim 1 wherein R R R and R are hydrogen; R and R are selected from hydrogen and alkyl of from 1 to 3 carbon atoms; R and R are alkylene having from 1 to 3 carbon atoms; R and R are selected from alkyl having from 3 to 10 carbon atoms and cycloal-kyl, A and A are hydrogen and n is an integer having a value of from 1 to 6.

3. A composition of claim 2 wherein R is alkyl having from 8 to 16 carbon atoms and -R and R are hydrogen.

4. A composition of claim 3 wherein n is an integer having a value of from 2 to 6 and R is alkyiene containing from 1 to 3 carbon atoms.

5. A composition of claim 4 wherein R is aikylene containing 2 carbon atoms. 5

6. A composition of claim 4 wherein M is zinc.

7. A composition of claim 5 wherein R is nonyl and M is zinc.

References Cited 10 10/1965 Hinka'mp 252-52 X 11/1965 LeSuer 252-515 X 11/1965 Norman et a1. 252-515 X 9/1966 Norman et a1. 252-515 X 12/1966 Ecke et a1. 252-52 X 5/1967 Hunter et a1. 252-52 X 5/1967 OShea 252-52 X FOREIGN PATENTS 1/1964 Great Britain.

3/ 1964 Great Britain.

3/ 1965 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

PATRICK P. GARVIN, Examiner.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pcenc No. 3,385,790 Da d May 28, 1968 Inventor(s) Henry M. Davies and Arthur S. Thomas It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 5, "Company, a corporation of Delaware" should read Chemicals Limited, London,

England, a British company SIGNED AND SEALED OCT 2 1 19 U Am Edmriillflcwhmlr. m. R- officcr flomiaqioaer of Patents 

